The present invention is directed to a tunable wavelength monitor/locker for use with more than one wavelength, more particularly to an non-etalon wavelength locker which can be placed in an optical path of an application beam or in an optical path of a monitor beam. More particularly, the non-etalon wavelength locker borrows from phase shifting interferometry to realize continuous operation, for example, using a patterned aperture to shift created interference patterns. A single patterned aperture used in conjunction with a reference signal may also simply replace an etalon in a conventional wavelength locker.
Some radiation sources exhibit wavelength drift over time in excess of that tolerable for many applications. This drift becomes increasingly important as the lifetimes over which these radiation sources are to be deployed increases. Factors such as temperature, age, operating power level, etc., all affect the output wavelength. By monitoring at least one of the direction of the wavelength change, the degree of the change and the percentage of the light being radiated at the different wavelengths, any or all factors which may be causing this change can be modified in accordance with the monitored signal via a feedback loop to stabilize the wavelength of the radiation source. Preferably, both the power and the wavelength are monitored in accordance with known techniques.
Such monitoring and stabilizing systems typically involve using a unit which is external to the radiation source itself. Such external units include crystal gratings, fiber gratings, spectrometers, and Fabry-Perot etalons, both straight and inclined. The grating systems include relatively large control units external to the radiation source. While etalon-based systems offer a more compact solution, so far these etalons are still separate units which may become improperly aligned, either with photodetectors or with optical elements required to direct and control the light onto the photodetectors.
Etalons are very expensive, due to the tight requirements thereon to insure proper performance thereof. This expense is even further increased when the etalon is to be miniaturized. Thus, it would be advantageous to create a wavelength locker which did not rely on an etalon and which can provide continuous monitoring over an operational range.
The present invention is therefore directed to a wavelength monitor/locker which substantially overcomes one or more of the problems due to the limitations and disadvantages of the related art.
The present invention may be realized by providing a wavelength detector including an optical structure receiving an input beam, the optical structure outputs at least three wavelength dependent two-beam interference signals, each wavelength dependent two-beam interference signal having a different phase offset. A detector receives the at least three wavelength dependent two-beam interference signals and outputting an electrical signal representative of each wavelength dependent two-beam interference. A processor receives the at least three electrical signals from the detector and generating a composite control signal.
The processor may use phase shifting interferometric techniques to generate the composite control signal. The optical structure may include a patterned aperture introducing the phase difference between the wavelength dependent two-beam interference signals.
The present invention may also be realized by providing a wavelength detector including a partial reflector receiving a beam from a light source, a patterned aperture, and a retro-reflector. A first portion output from the partial reflector is directed to the patterned aperture and a second portion output from the partial reflector is directed to the retro-reflector. The retro-reflector directs the second portion to the patterned aperture such that the first portion and the second portion interfere. A detector receives interfering signals from the patterned aperture, the patterned aperture outputting at least two periodic signals offset from one another.
The present invention may also be realized by providing a wavelength monitor which monitors a wavelength of a beam, the wavelength monitor including a first detector, a second detector, a third detector, a first filter in an optical path upstream of the first detector, a second filter in an optical path upstream of the second detector, a third filter in an optical path upstream of the third detector, the first, second, and third filters having different filter properties from one another. An optical element directs at least a portion of the beam onto each of the first, second, and third detectors through the first, second and third filters, respectively. A processor receives outputs from the first, second and third detectors, and determines the wavelength of the beam.
At least one of the first, second, and third filters may be a patterned aperture receiving two beams incident thereon. Each of the first, second, and third filters may be a patterned aperture receiving two beams incident thereon, each patterned aperture being different from the others. Each patterned aperture may have the same basic pattern and is out of phase with each of the other patterned apertures. Each may be out of phase with another aperture by the same amount. Phase differences between patterned apertures may cover 2xcfx80.
A wavelength monitor which monitors a wavelength of a beam, said wavelength monitor including a first detector receiving a first signal, a second detector receiving a second signal, and a third detector receiving a third signal. At least two of the first, second, and third signals are periodic with respect to wavelength and a set having a value for each of the first, second and third signals represents a unique wavelength within a continuous operational range.
An optical element directs at least a portion of the beam onto each of the first, second, and third detectors. A processor receives outputs from the first, second and third detectors, and determines the wavelength of the input beam.
These and other objects of the present invention will become more readily apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating the preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.